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Ever noticed how snow will disappear without melting? Even in sub-freezing weather, the frost on your car or the snow bank will get smaller. How does this happen? It’s called sublimation. Bob explains …
On a cold sunny day, you may have noticed that the huge piles of snow pushed onto the edges of parking lots by plows sometimes look as if they’re steaming. This is one sign that sublimation is underway.
The snow is turning from a solid directly to a gas, bypassing the liquid watery stage.
Sunny snowfields shrinking and eventually vanishing without melting into water.
Snowmen starting to shrink even though there’s still snow on the ground.
Snow disappearing from your roof even though it’s too cold to melt.
The snow on your picnic table in the backyard going down even though it’s not melting.
Ice cubes shrinking in the freezer.
All due to ice turning directly into vapor without having to first melt.
If your home’s walkway or driveway has gotten a thin coating of ice and snow and you’d rather not use salt, just leave it alone. If the air is dry, as it usually is this time of year, and especially if it’s sunny, all that white stuff will go away by itself. Even if it never melts.
This is because water molecules will happily go from their liquid or solid phase into their gaseous phase; the only thing that’s required is that they’re moving fast enough. Each molecule jiggles at a particular speed and in a huge mass of them, some are always moving fast enough to escape the water or ice and join their gaseous buddies in the atmosphere.
Dry air accelerates this phase change. So does sunlight, since water molecules readily absorb the sun’s infrared, which makes them jiggle faster. Solar infrared is also why the interior of your car heats up when parked in sunlight.
It’s fun when snow and ice sublime. And yes, that’s an actual verb.
Bob Berman, astronomer editor for The Old Farmer’s Almanac, covers everything under the Sun (and Moon)! Bob is the world’s most widely read astronomer and has written ten popular books. Read More from Bob Berman